Generally, an alkali battery such as a nickel metal-hydride battery, nickel-cadmium battery, etc., has a power generating element placed within a battery case which serves as a terminal of one electrode. For example, an exemplary battery shown in FIG. 50 has been proposed where an current collecting plate comprises a current collecting plate 101 and a current collecting lead 103 which has the same thickness with the former and an elongated body are integrally fabricated.
In a battery as described above, as shown in FIG. 51, a power generating element containing three sheets one acting as a positive electrode plate 8, the other as a negative electrode plate 9 with a third sheet acting as a separator 10 being interposed between the foregoing two sheets which are winded into a roll is placed in a metal battery case 6 which serves as a packaging container, a current collecting lead 103 is connected by welding to a sealing body via a single welding point, after that the sealing body 11 is joined to the battery case 6 with an insulating gasket to seal.
When such an alkali battery is applied to drive electric motor-driven tools and electric vehicles which require a high rate charge/discharge cycle, the electric resistance of a current collecting plate and lead connecting between a power generating element and a sealing body is a particularly important factor which greatly affects the performance of the battery. In those applications, the battery is often required to repeat charge/discharge cycles by high current, and to meet the requirement it is necessary to minimize the internal resistance in those use.
The battery in which the internal resistance is minimized includes, for examples the one disclosed in Japanese Unexamined Patent Application Publication No. 2004-63272 (FIGS. 1 to 4, 10, and 11, and paragraphs [0022] to [0038]).
The structure disclosed in the above patent document which enables the minimization of internal resistance will be described below by referring to a nickel-cadmium battery as an example.
FIG. 52 is a perspective view of a nickel-cadmium battery with some parts of interest emphasized in which a current collecting plate has been integrally made by punching. FIGS. 53(a) and 53(b) are the flat and sectional views of the current collecting plate 1. The current collecting plate is made of a nickel-plated iron plate having a thickness of 0.3 mm, and comprises a flat portion 2 and a protruded portion 3 which has been made by punching to have a height of about 2.0 mm.
The current collecting plate has an approximately disc-like shape, and comprises the protruded portion 3 which has a thinned top 4 to serve as a welding point.
The flat portion has holes 5 formed there through. Each hole has fins 52 directing downward along its peripheral margin. Those fins serve as welding points in contact with a positive electrode plate. FIG. 41 is a sectional view of a electrode assembly which will be connected via the current collecting plate 1 above to a sealing body after the electrode assembly is placed in a battery case 6 serving a packaging container.
This nickel-cadmium battery is obtained, as shown in FIG. 54, by placing a battery element comprising a nickel positive electrode plate 8 and a cadmium negative electrode plate 9 with a separator 10 interposed between the two electrode plates all winded into a roll, in a battery case 6 in the form of a cylindrical body with a bottom, putting a current collecting plate 1 as described above on top of the assembly, and connecting a sealing body 11 to the current collecting plat 1 by direct welding via a protruded portion 3.
The sealing body 11 comprises a lid body 12 having a downward directed protrusion circular in contour on its bottom surface, a positive electrode cap 13, and a valve body interposed between lid body 12 and positive electrode cap 13 which consists of a spring 15 and a valve plate 14. The lid body has a vent hole 16 formed at its center.
Before being welded to the sealing body, the current collecting plate 1 is welded to the nickel positive electrode: during this operation, fins 5B protruding backward from the peripheral margin of each hole 5 formed through the flat portion 2 of current collecting plate 1 serve as a welding point. On the other hand, a negative electrode current collecting plate 7 in the form of a disc is placed on the bottom of battery case 6, and connected by welding to the negative electrode plate 9. The open-end portion 11 of battery case 6 is sealed by caulking.
Since the current collecting plate 1 is configured as described above, it is readily possible to provide secure welding points on the disc-shaped metal plate simply by punching the plate, which allows the establishment of secure, reliable connection points.
Since the flat portion 2 connects to an current collecting body which in turn connects to an electrode, and protruded portion 3 serves as a current collecting lead connected to a positive electrode terminal represented by a sealing body, it is possible to integrally fabricate the two portions which permits the reduction of resistances at connection joints.
As shown in FIG. 53(b), each protruded portion 3 has a thinned top surface 4 where electric current can concentrate during welding. In addition, since the thinned top surface is elastic, pressure imposed during welding is securely transmitted to the welded area which will ensure secure connection.
According to the battery configured as above, it is certainly possible to reduce the length of lead. However, lead connections are possessed of a number of problems. Since the welded area is beneath the positive electrode cap 13, and the lead must be welded to the thick lid, heat generated during welding will escape to the lid, which will degrade the assuredness y of welding, and cause variation in welding. It is necessary for the same reason to flow a big current through a single welding point, which will disable the formation of multiple welding points, and thus the establishment of a sufficiently low internal resistance.
Other batteries in which the internal resistance is minimized are cited, for example, in Japanese Examined Patent Application Publication No. 2001-345088 (FIG. 2, and FIG. 55 of its Application), and Japanese Unexamined Patent Application Publication No. 2001-155710 (FIGS. 3 and 4, and FIGS. 56 and 57 of its Application).
The battery described in the former patent document in which the internal resistance is minimized is a battery stack. The battery stack comprises, as shown in FIG. 55, one unit cell B connected to a second unit cell A with a sealing plate 7 of the former being contacted with the bottom of a packaging can 6 of the latter. The unit cell B has an annular joint member 10 which has an aperture at a position corresponding to the cap 8 provided on the sealing plate 7. The annular joint member 10 comprises an annular base portion 11 which has an internal radius smaller than the internal radius of packaging can 6, and a convex portion 12 which has, in profile, a peak and trough, and a projection portion 12 which projects from the trough like a cone. Thus, the current collecting passage between the unit cell A and unit cell B has a length equal to the distance between
According to the battery described in the former patent document, a welding point on top of a knob 13 of a ring-like connecting member 10 is outside the periphery of cap 8, but the ring-like connecting member 10 is for connecting a sealing plate of one battery to the bottom of a packaging can of another battery. Thus, its position does not necessarily suggest the preferred positional relations between two welding points formed one at a lead and the other at a sealing plate, one at a current collecting plate and the other at a lead, and one at a current collecting plate and the other at the bottom of container within a battery.
The battery described in the latter patent document in which the internal resistance is minimized comprises, as shown in FIGS. 56 and 57, a battery case 16 comprising an open end which serves also as one electrode, and a sealing body 17 (lid body 17a, positive electrode cap 17b, spring 17c, and valve body 17d) which hermetically seals the open end and serves as the other electrode, and an electrode assembly 10 in which a positive electrode plate 11 and one terminal of negative electrode plate 12 which is connected to an current collecting plate 14, are housed in the battery case 16, wherein the sealing body 17 and current collecting plate 14 are connected by bonding via a lead portion in the form of a thin-bellied drum body 20. Along both the upper and lower flange portions of drum body 20, there are formed alternately broad edge portions 22a, 23a and narrow edge portions 22b, 23b. The two kinds of edge portions of the upper and lower flanges of drum body 20 are arranged as follows. When view from up downward, the broad edge portion 22a overlaps with narrow edge portion 23b below with a space in between. Similarly, the narrow edge portion 22b overlaps with broad edge portion 23a below with a space in between.
The nickel-hydrogen storage battery having a lead portion comprising a drum body 20 as described above is assembled by welding in a manner as described below.
For assembling a nickel-hydrogen storage battery, first, a drum-like cylinder 20 as described above is placed on top of a current collecting plate of positive electrode 14, a welder electrode (not shown) is placed on the narrow edge portions 22b of upper flange portion, and the broad edge portions 23a of lower flange portion axe connected by spot welding to the current collecting plate 14. Then, an electrode assembly 10 in which the broad edge portions 23a has been connected by welding to the current collecting plate of positive electrode 14 is placed in a battery case with a bottom made of nickel-plated iron 16 (the outer surface of the base serves as an external terminal of a negative electrode) (paragraph [0025] of the last-mentioned patent document).
After a sealing body 17 is put into place as described above, one welder electrode 1 is applied to the upper surface of positive electrode cap (external terminal of positive electrode) 17a, while the other welder electrode 2 is applied to the lower surface of the base of battery case 16 (external terminal of negative electrode). While a pressure of 2×106 N/m2 is applied between the pair of welder electrodes W1, W2, a voltage of 24 V is applied across the welder electrodes W1, W2 in a discharging direction to allow an electric current of 3 kA to pass for about 15 msec. During this operation, current is concentrated to contact points between the base of sealing body 17 and knobs 22c formed on the broad edges 22a of upper flange portion 22, and thus the knobs 22c and the base of sealing body 17 are joined by welding to form welding joints. At the same time, contact points between the lower surface of negative electrode current collecting plate 15 and the upper surface of bottom (external terminal of negative electrode) of battery case 16 are joined by welding to form welding joints (supra, paragraph [0027]).
Next, an insulating gasket 19 is applied to the margin of sealing body 17, and a pressure is applied to the sealing body 17 with a presser to push the insulating gasket 19 into the interior of battery case 16 until the lower end of insulating gasket 19 reaches as far as an annular constriction 16a. Then, the open end of battery case 16 is caulked inward to seal the open end, to produce a cylindrical nickel-hydrogen storage battery having a claimed capacity of 6.5 Ah. Incidentally, as a result of pressure applied during this operation, the cylindrical drum body 20 becomes flat with its thin belly portion 21 being totally collapsed (supra, paragraph [0028]).
An alternative method to produce a cylindrical nickel-hydrogen storage battery having a claimed capacity of 6.5 Ah is disclosed which comprises welding before and after the closure of the open end of battery case. The method is as described below.
A drum-like cylindrical body 20 as described above is placed on top of a current collecting plate of positive electrode 14; a welder electrode (not shown) is applied to the peripheral margin of narrow edge portions 22b of upper flange portion 22; and the broad edge portions 23a of lower flange portion 23 and the current collecting plate 14 are joined by spot welding. Then, an electrode assembly 10 in which the drum-like cylindrical body 20 has been connected by welding to the current collecting plate of positive electrode 14 is put into a battery case 16 (its outer surface serves as an external terminal of negative electrode) with a bottom which is made of nickel plated iron (supra, paragraph [0029]).
Next, an insulating gasket 19 is applied to the margin of sealing body 17, and a pressure is applied to the sealing body 17 with a presser to push the insulating gasket 19 into the interior of battery case 16 until the lower end of insulating gasket 19 reaches as far as an annular constriction 16a. Then, the open end of battery case 16 is caulked inward to seal the open end. Incidentally, as a result of pressure applied during this operation, the cylindrical drum body 20 becomes flat with its thin belly portion 21 being totally collapsed. Then, one welder electrode W1 is applied to the upper surface of positive electrode cap (external terminal of positive electrode) 17a, while the other welder electrode W2 is applied to the lower surface of the base of battery case 16 (external terminal of negative electrode). (supra, paragraph [0031]).
Then, while a pressure of 2×106 N/m2 is applied between the pair of welder electrodes W1, W2, a voltage of 24V is applied across the welder electrodes W1, W2 in a discharging direction to allow an electric current of 3 kA to pass for about 15 msec. During this operation, current is concentrated to contact points between the base of sealing body 17 and knobs 22c formed on the broad edges 22a of upper flange portion 22, and thus the knobs 22c and the base of sealing body 17 are joined by welding to form welding joints. At the same time, contact points between the lower surface of negative electrode current collecting plate 15 and the upper surface of bottom (external terminal of negative electrode) of battery case 16 are joined by welding to form welding joints (supra, paragraph [0032]).
The battery disclosed in the last-mentioned patent document is fabricated as described above. In the battery, since the welding points formed between the bottom surface of sealing body 17 and knobs 22c on the broad edge portions 22a of upper flange portion 22 of drum-like cylindrical body 20 are, in a flat view, outside the periphery of positive electrode cap 17a, it will be safely concluded that the resistance of sealing body is reduced.
However, with this battery, the drum-like cylindrical body 20 is made flat with its thinned belly 21 collapsed in the presence of pressure applied during closure of the open end of battery case, and the welding points between the base of lid body 17 and the knobs 22c on broad edge portions 22a of upper flange portion 22 of the drum-like cylinder 20 are displaced, in a flat view, so much from the welding points between the broad edge portion 23a of lower flange portion and the current collecting plate 14 that lead extending from the welding points formed between the inner surface of sealing body (lid) and drum-like cylindrical body 20 (lead) to the most adjacent points among the welding points formed on the current collecting plate has a considerable length. Thus, arrangement of those welding points is not sufficient for producing a significantly lowered electric resistance.
Usually, the welding point between the lower surface of negative electrode current collecting plate 15 and the upper surface of the bottom of battery case 16 (external terminal of negative electrode) is at the center or, in a flat view, beneath the positive electrode cap 17a. However, according to the configuration of this battery, the upper welding points are considerably displaced, in a flat view, from the lower welding points, arrangement of those welding points is not sufficient for producing a significantly lowered electric resistance.